Measles fear grows in Silicon Valley

The nationwide measles outbreak that started at Disneyland in Southern California is now hitting home in the tech community in Northern California, with word this week that a LinkedIn employee in the San Francisco office may have exposed hundreds of Bay Area commuters to the disease. Meantime, at least one operator of day care centers in Silicon Valley is urging parents to make sure their children's vaccines are up to date.

LinkedIn said it learned on February 10 that one of its employees had been diagnosed, and immediately notified all of its 7,000 employees worldwide. But the unidentified employee had already made multiple trips on Bay Area Rapid Transit between February 4th and 6th, and had eaten in a San Francisco restaurant on the 4th.

"We are working very closely with the San Francisco Department of Public Health, and following their recommended protocol for managing this situation," LinkedIn spokesman Hani Durzi said in a statement. "The health and well-being of our employees is our absolute top priority, and we will take whatever steps are advised to ensure their safety and the safety of the general public."

The large concentration of young parents working at the region's technology firms has brought the measles outbreak into focus.

Wired Magazine, citing California Department of Health data, reported this week that several on-site day care facilities at technology firms have vaccination rates too low to provide the so-called "herd immunity" that is supposed to keep the disease from spreading.

Experts generally say if 92 percent of the community is vaccinated, it should be enough to protect the general population, though some caution the figure should be more than 95 percent.

But Wired found rates as low as 59 percent at a Cisco Systems facility in San Jose, and 68 percent at a Google facility in Mountain View. CNBC verified the figures in the state database.

Both companies say the numbers represent a snapshot of data, and may not reflect the most recent immunization history reported by parents. Google notes that in 2013-14, the facility in question had an 81 percent immunization rate. And Cisco says it continually works with its employees and daycare contractors to make certain records are up to date.

"The health and well-being of the children, families and staff at Cisco childcare facilities are a top priority," spokeswoman Robyn Blum said in a statement.

Bright Horizons, which provides on-site day care services for several tech firms in the region, urged parents in a letter dated February 6 to make certain that both their children's and their own vaccinations are kept up to date, particularly the MMR (measles, mumps, rubella) vaccine.

"We want to protect everyone in our centers from the serious risks posed by measles and the best way to do that is to make sure that as many people as possible are vaccinated," the letter said.

Low vaccination rates at a few facilities are not necessarily a problem, UCLA pediatric infectious disease specialist Dr. James Cherry told CNBC in an interview, but the more unvaccinated people there are, the greater the risk.

"We've always had these little pockets, and through the years we've had unvaccinated travelers go to other countries come back and find all these people in these schools, but it didn't go anywhere because the rest of the population had good levels of immunity," he said.

Now, that is increasingly not the case—not just in daycare facilities, but in schools and workplaces. As a result, he said, the outbreak is likely to spread.

"We're in a situation now where for various reasons we're not anywhere near where we should be," he said.